A wind turbine comprises a wind turbine tower, a nacelle mounted on top of the wind turbine tower, wherein a shaft is supported in a bearing and can rotate within the nacelle. The wind turbine shaft has one or more wind turbine blades connected to it and drives an electrical generator. The rotor blades may be turned or rotated or adjusted around their longitudinal axis, in order to adjust a rotor blade pitch angle, being an angle between a cord line of the rotor blade and a rotor plane being a plane perpendicular to the axis of the shaft which is driven by the rotor blades. For example, when the rotor blade pitch angle is zero, the rotor blades may be adjusted to transfer a maximal amount of wind energy of wind impacting on the rotor blade, in order to produce maximal amount of electrical power. In contrast, when the rotor blade pitch angle is 90°, the impacting wind (assumed to impact in a direction parallel to the rotor axis) will not drive the rotor blades and thus the wind turbine will not produce any energy.
During operation of the wind turbine, it may be required to adjust the pitch angle depending on a rotational speed of the rotor, in dependence of a desired power output (in particular including active power and/or reactive power) and other requirements. Thereby, a pitch servo system may be involved for adjusting the rotor blade pitch angles. However, the pitch servo system may have a fault and may incorrectly adjust the rotor blade pitch angles. In case of such a fault, there may be a risk of damaging components of the wind turbine.
Conventionally, if a fault of the pitch servo system is detected, a safety system is activated and may stop the turbine in a safe manner. In a conventional wind turbine, a safety system may be activated when the rotor speed reaches or exceeds a speed limit. However, it has been observed that detecting a pitch servo system fault in the conventional manner is not reliable in all situations, involving the risk of missing a pitch servo system fault and thereby involving the risk of damaging components of the wind turbine.
There may be a need for a method and for a system for detecting a rotor blade pitch angle adjustment fault which is more reliable than the conventional methods and arrangements and may reduce damaging components of the wind turbine.